Platelet-derived growth factor, PDGF, is a polypeptide hormone capable of initiating processes involved in wound healing, atherosclerosis and the development of malignancy. Intracellular events influenced by PDGF include collagen and prostaglandin synthesis, oncogene expression, phosphatidylinositol turnover, tyrosine phosphorylation and intracellular calcium levels. Studies currently involve the mitogenic and chemotactic effects of PDGF-like proteins produced by osteosarcoma and vascular cells. In order to pursue these studies it would be extremely useful to obtain an antiserum which recognizes a defined region of biologically active, unreduced PDGF. Since it is not practical to purify PDGF in the quantity needed to develop an anti-PDGF serum, an alternative approach is presented here. Synthetic peptides based on the amino acid sequence of PDGF will be synthesized. These peptides will be constructed so that the secondary structure is stabilized by intrachain disulfide bridges. This approach has been successfully used to develop an antiserum which cross reacts with a synthetic peptide and a native Hepatitis B antigen. We propose to synthesize four distinct PDGF peptides, which will be injected into rabbits to generate a polyclonal antiserum. Rabbit antiserum will then be tested for recognition of the synthetic peptide and native PDGF.